Marantz 2250b tone board

[pjf610]

Hi all, Need some help, I have been working on my 2250b and going through some testing I seem to have a weak left channel on the tone board. I plug my phone directly into the Main in and get great sounds out of both Land R channels but when i go to use the FM or other functions the left channel is very weak, I replaced the cap's on the board I had one bad BA312 IC replaced that but still no luck I checked all the resistors they are good checked all the caps I replaced they are good, any advise??

Pat

 

[bryans12v]

1.You have a weak channel with your phone plugged into main in on FM?

2.What led you to believe the BA312 IC was bad?

3. Was this problem present before you started working on the unit?

 

[pjf610]

Both channels were fine with my phone plugged into the main in
I checked the trace from pin 5 on the plug in connector and did not get a reading on 1 BA312 across those pins I got readings on the other BA312
The left channel was weak

 

[bryans12v]

Couple things to check out...

Make sure you've cleaned all the switches well, I always do two cleanings. Also clean the pre out main in connections. Use a signal generator app and use a sine wave to the aux input. This will help keep the voltages stable while testing. From here measure the ac voltage at the pre-out RCAs on the back to see what your signal voltage looks like and compare L & R. Now you can work your way back till they're both even. Having a scope here helps by making the sine wave visible.

Now check these on JH10 and JH11 just to confirm the wiring from the filter switch board is good.

Next check JH06 and JH07 (l/r signal input to filters) to verify the problem isn't on the filter switch assembaly. If these are still off check pin 6 and 7 on the tone amp connector to verify your issue is still present. If so, check the input to the tone board from your volume pot and balance slider. You can check the volume pot and balance slider with a resistance measurement to make sure they're operating properly.

Good luck.

 

[pjf610]

Get back on Mon.

 

[pjf610]

Hi guys, the 2250b is back to life I replaced the BA312 and it came alive I wish to thank you all for your help, now on to my next project a 2270
Thanks again